[英]An efficient way of finding pairs of sets in a set of sets
我有一組集合:{1,2,3...},我想找到所有滿足 ∩≠∅ 的對 (, )。
我能想出的唯一方法是重復條件檢查 Σ 時間。
如果我可以用類似 python 的偽代碼來表示它:
from copy import deepcopy
setA = {A1, A2, A3, A4....}
setACopy = deepcopy(setA)
intersectingPairs = set()
for Ai in setA:
for Aj in setACopy:
if isIntersect(Ai, Aj):
intersectingPairs.add((Ai, Aj))
setACopy.remove(Ai)
我希望隨着setA
的大小增加,這將非常耗時。
有沒有更好的算法可以參考?
您可以線性解析數據以構建查找表,而不是單獨檢查每一對。 如果連接稀疏,這可以很快產生您想要的唯一對。
from itertools import combinations
from collections import defaultdict
from pprint import pprint
A1 = {1, 2, 3}
A2 = {2, 4, 6}
A3 = {1, 3, 5}
A4 = {2, 3, 5}
A5 = {8, 9}
# Change them to tuples so they are hashable
superset = set((tuple(subset) for subset in [A1, A2, A3, A4, A5]))
# build families of all sets with a specific element
lookup = defaultdict(list)
for subset in superset:
for element in subset:
lookup[element].append(subset)
# If the families are small, brute force from there
pairs = set()
for __, family in lookup.items():
for result in combinations(family, 2):
pairs.add(result)
pprint (pairs)
如果連接不是稀疏的,這甚至可能比查看每一對更糟糕。 但如果它們很稀疏,它可能會非常快。
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